The present invention relates to a method of manufacturing high conductive sinters and more particularly to a method of manufacturing high conductive sintered products made of conductive lanthanum.chromium composite oxide materials.
Although a composite oxide sinter including lanthanum oxide (La.sub.2 O.sub.3) and chromium oxide (Cr.sub.2 O.sub.3) is normally a high resistor, a composition wherein one portion of the La ion within the lanthanum oxide is a solid-solution-substituted by a Sr ion or a Ca ion and sintered in an oxidation atmosphere is known as a conductive composite oxide which has a specific resistance ranging from several .OMEGA.cms to several tens .OMEGA.cms. However, the sintering operation of the composite oxide of these conductive La.sub.2 O.sub.3.Cr.sub.2 O.sub.3 materials, which is usually performed at temperatures of 1,700.degree. C. or more, or made by a hot press operation in the temperature range of 1,600.degree. to 1,700.degree. C., requires such extremely high temperatures that the sintering properties of the resultant material is often inferior and it is extremely difficult to manufacture sintered materials of good characteristics.
It is well known in fact that, in the case that the composite oxide of the conventional known La--Cr combination is a composition wherein one portion of the La ion is solid-solution-substituted by a Sr ion and is sintered in an oxidation atmosphere, namely, 1 to 60% of La ion of (La.Sr)CrO.sub.3 is substituted by an Nd or Y ion; 1 to 20% of a Cr ion is substituted by a Co ion, 1 to 60% of an La ion is substituted by an Nd or Y ion or 1 to 20%, of a Cr ion is substituted by a Co ion, the sintering properties and conductive properties of such materials are not improved when the substitution amount is 1% or less, respectively. In addition thereto, when the solid-solution-substitution-amount of the La ion by an Nd or y ion exceeds 60%, the conductive properties are undesirably lowered, and when the solid-solution-substitution-amount of the Cr ion by the Co ion exceeds 20%, the heat-resisting properties are undesirably lowered. To eliminate the above disadvantages of the known method, according to the present invention, the solid-solution-substitution-amount of La by Nd or y is restricted to within the range of 1 to 60% and the solid-solution substitution-amount of Cr by Co is restricted to within the range of 1 to 20%.